in recent years, only four airlines, american, delta, united and southwest, would be left with 70% of the u.s. market. while airfares haven't risen much in recent years, experts worn, less competition could ultimately drive up prices. >> if you're looking out over the next three or four years of your vacation plans you'll average between 5 and 10% increases year over year once you hit 2014. >> concerned about the overall number of flights available, the cost of those flights. >> more and more mergers, prices are worse, choices are less. doesn't add up. >> reporter: for now, both usairways and american will continue to fly independently. passengers will fly the airline on which they're booked. and until the merger is complete, the frequent flier programs will remain separate. ultimately, a combined frequent flyer program could include tens of millions of people with more destinations to choose from, but all competing for that upgrade or the free trip. tom costello, nbc news, washington. >>> there is news tonight from the world of science. and this could be a day that lasts in medical history.